My guess for EKU8:
- It takes TA18-TA23 from the connector
- It subtracts the base address for the ROM, 0x180000 in byte or 0xC0000 in words, from the high address lines and produces new address lines TA18-TA21 going to the T-ROM
- It checks if the address is in the 8MB range of the ROM and generates the OE signal for the built-in T-ROM on pin 19 and the cart T-ROM on pin 18
Update:
With a bit of python and a Quine-McCluskey solver I arrive at:
TA18_I = (NOT TA1
TA19_I = (((NOT TA1
AND TA19) OR (TA18 AND (NOT TA19)))
TA20_I = (((NOT TA19) AND (NOT TA20)) OR (TA18 AND TA19 AND TA20) OR ((NOT TA1
AND (NOT TA20)))
TA21_I = ((TA18 AND TA19 AND TA21) OR TA22 OR (TA20 AND TA21))
OE_CART = (((NOT TA19) AND (NOT TA20) AND (NOT TA21) AND (NOT TA22)) OR (TA18 AND TA19 AND TA22) OR TA23 OR (TA21 AND TA22) OR ((NOT TA1
AND (NOT TA20) AND (NOT TA21) AND (NOT TA22)) OR (TA20 AND TA22))
OE_INT = (TA22 OR TA21 OR (TA18 AND TA19) OR TA23 OR TA20)
... probably a bit much for discrete logic, but I have no idea how close my guess is to the real expression.
Update:
I resurrected my window xp machine to use my genius g540, only to find out it doesn't work with 27c322. Doh! To get at least some use out of it I tried to read the PAL from KOVSH:
I took the pinout for a 28c16, connected the address lines to the inputs and the data lines to the output. The result are those two binary files in the zip.
Results:
EKU8 seems to work pretty much as predicted above. The only surprise is U8 pin 7/J2 pin 29: The enable lines are only generated when it is 1. This is strange, because if this is an address line I would expect it to be 0, as the tile roms are loaded to the start of the address space, if this was OE it would be 0 because enable is active low. Weird. Maybe I made a mistake reading it, though.
EKU7 subtracts 1 from A19/A20 and generates the enable lines for U1-U6: U1 and U3/U4 are enabled for output 0, U1 and U4/U5 are enabled for output 1, U1 and U2 are enabled for output 2. Interestingly 3 doesn't seem to be decoded? Any input lower than 1 or higher than 3 disables all OE.
ASIC 5 and 4 seem to be A19 and A20, I guess ASIC 3 and 2 are A21 and A22.
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